Aspotless day is a day without sunspots, a day when the face
of the sun is utterly blank. Spotless days never occur during Solar
Max when the sun is active, but they are common during solar minimum,
the opposite phase of the 11-year sunspot cycle when the sun is
very quiet. By counting spotless days, we can keep track of the
depth and longevity of a solar minimum.

By
the standard of spotless days, the ongoing solar minimum is the
deepest in a century: NASA
report. In 2008, no sunspots were observed on 266 of the year's
366 days (73%). To find a year with more blank suns, you have to
go all the way back to 1913, which had 311 spotless days (85%):

The
lack of sunspots in 2008, made it a century-level year in terms
of solar quiet. Remarkably, sunspot counts for 2009 have dropped
even lower. As of March 31st, there were no sunspots on 78 of the
year's 90 days to date (87%).

On
the front page of spaceweather.com, you can monitor the increasing
number of spotless days. Look beneath the Daily Sun image for these
key indicators (updated daily):

Current
stretch: 9 days Updated April 4, 2009

"Current Stretch" is the number of consecutive days the
sun has been blank. The 100-year record is 92
consecutive spotless days in April, May and June of 1913.

2009
Total: 81 days (87%) Updated April 4, 2009

"2009
Total" is the total number of days and the percentage of days
in 2009 that the sun has been blank. The 100-year record for a full
year is 311 spotless days (85%) in
1913.

Since
2004: 592 days Updated April 4, 2009

The
first blank sun of the ongoing solar minimum appeared in 2004. "Since
2004" tells us the total number of spotless days since that
time. The 100-year record for total spotless days in an entire multi-year
minimum is 1019 spotless days in the
years around 1913.

Typical
Solar Min: 485 days

Looking
back at the last ten solar minima (not including the ongoing minimum),
we can count the total number of spotless days in each and calculate
an average: 485 spotless days. The
average exceeds the number of days in a year because solar minima
last much longer than one year. The fact that the ongoing solar
minimum has already racked up 590+
spotless days with no end in sight tells us that it is much deeper
and longer than average.

This
page will be updated with more information and data in the days
ahead.